The invention relates to a tomographic x-ray apparatus for producing transverse layer images of a radiographic subject, with an x-ray measuring arrangement comprising an x-ray source producing a fan-shaped x-ray beam penetrating the radiography subject, the crosssectional extent of this beam, perpendicular to the layer plane, being equal to the layer thickness, and, in the layer plane, being of such a magnitude that the entire radiographic subject is penetrated, said measuring arrangement further including a radiation receiver which determines the intensity of radiation behind the subject, with a drive system for the measuring arrangement for producing rotational movements, and with a measured value converter for the transformation of the signals supplied by the radiation receiver into a layer image, wherein the radiation receiver consists of a series of detectors, these detectors being connected at one terminal to a common power supply installation, and the number of detectors being selected in accordance with the desired picture resolution (or definition).
It is known to employ as a measured value source for the measured value converter, xenon-detectors connected to a high voltage source and functioning as ionization chambers. Thus, per angular position of measuring arrangement (1, 2), all image points of the angular position are simultaneously measured via a corresponding number of individual x-ray detectors, and the signals of the detectors are further processed in parallel in individual measuring channels. In a measuring arrangement such as this, various types of errors occur; one type being the so-called additive errors in measurement brought about by high voltage instability. In utilizing xenon-detectors, every change in the common operating high voltage produces a displacement current due to the detector capacitance. This displacement current is superimposed on the x-ray measuring signal as an additive error. Particularly interfering are those high voltage changes which do not die down again or which only die down incompletely during the measuring interval, since, subsequent to differentiation at the detector capacitance, these interferences have as a consequence displacement currents which are not or are only partially cancelled out.